A Feasibility Study - Aaltodoc - Aalto-yliopisto

8.2.3 Pressure loss
Due to the fact that the WEC is situated out at sea, the pressurized seawater will have to
travel, depending on the location, a distance of roughly 50 – 500 m until it reaches the
shore. The movement is twofold: distance to shore and the increase in elevation, which
is usually 5 – 20 meters for WaveRoller, as it is situated nearshore. The pressure loss
due to these two movements will be analyzed next.
The energy needed to transfer the pressurized water vertically for the distance of 5 – 20
meters, results as a pressure change. The amount of pressure change can be calculated
from
where Δp is the pressure change, ρ the density of seawater, g the gravitational
acceleration and ΔH the difference in elevation. For AaltoRO this pressure change is
roughly 0,5 – 2 bar.
The pressure loss due to flow friction arising from the travelled distance from the WEC
to the shore can be calculated from
where λ is the friction factor, L the length of the pipeline, D the inner diameter of the
pipe, ρ the density of seawater and w the velocity of water in the pipe.
The velocity of water w can be calculated when the volume flow rate ̇ and the
dimensions of the pipe are known with the equation
where ̇ is the volume flow rate of water and A is the cross-sectional area of the pipe.
The friction factor λ can be determined from the Moody chart, which is a graph giving
the relations of the Reynolds number, relative roughness and the friction factor λ
(Moody 1944).
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̇
(3)
(4)
(5)